Hydraulic brake apparatus



y 9 E. e. CARROLL 2,003,247

HYDRAULIC BRAKE APPARATUS Filed Jan. 18, 1930 gnwntoz PatentedMsy28,1935

PATENT or ice 2 ,003,241 HYDRAULIC mum: mans-ms Eugene G. Carroll, by mesne Los Angelcs, Calif assignor,

entl,

toBendixBrakeCompany, South Bend, M, a corporation of Application 1.... s, 19:0, sci-n1 No. 421,736 r 3 Claims. ((1. "-54.0

This invention relates to hydraulic brake apparatus of the type disclosed in my Patent No. 1,770,064, dated July 8, 1930, now Reissue No. 19,432. This apparatus includes a master cyl- 6' inder with foot-operated means for developing hydraulic pressure in the cylinder and for communicating the same to the hydraulic brake devices located at the automobile wheels. In

devices at the wheels will always be completely full of the operating liquid.

If a single piston is employed in a cylinder having a chamber back of the piston, closed from the atmosphere, a partial vacuum will be produced in the rear end of the master cylinder and in order to overcome this difliculty a bypass port was provided leading around from the port to the chamber back of the piston tokeep this rear chamber full of liquid, and the rear chamber operated to catch any leakage of liquid past the piston. However, it was foundthat, as the compressing piston advances across the inlet port, even with the rear chamber full of the operating liquid, a partial vacuum is produced, causing a loss in pressure and tending to withdraw the operating liquid through the inlet port from the compression-chamber, thereby entailing a loss in pressure as the compressing piston advances across the inlet port.

In this way a loss in the volume of'liquid in ad-.

vance of the compressing piston occurred and an undesirable lost-motion effect occurred in the application of the brakes.

In my prior patent referred to above, I overcame this diiiiculty by providing a piston of larger diameter in the rear of the forward or compressing piston, and this piston developed pressure in a chamber of larger diameter, therebycausingariseoraboos"inthe pressure. of the liquid in the inlet port, operating "to prevent emux through this port, and perhaps actually causing an inflow of liquid through the inlet port into the compressingchamber as the forward piston advances. y Y

The construction disclosed in my patent referred to above involved theuse of a small chamber from which the inlet port led into the compression chamber, and into which a port from the rear,- or booster, chamber admitted liquid from the rear chamber; The development of pressure in the rear chamber tended to develop a flow back to the reservoir; in order to insure the pas'ssage of .the liquid from the rear chamber around to the forward or compression chamber and prevent any eiilux of liquid through the inlet port, it was desirable to employ a valve in the by-pass connection between the two ports, although the use of such a valve was not essential with pistons of equal diameter.

The general object of this invention is to provide a simple construction for a master cylinder of this kind which will not necessitate the use of a valve in the by-pass connection, nor pistons of different diameters, but which will operate to prevent the development of a partial vacuum at the back of the compressionpiston as it advances. 1 p

A further object of the invention is to provide means for insuring a plentiful supply of operating liquid to the master cylinder and the connected hydraulic system in which it develops pressure for applying the brakes. In the practical operation of hydraulic brakes the liquid often becomes quite hot and may boil out of the reservoir. One of the objects of this invention is to provide an expansionreservoir whicnwill operate to prevent this.

Further objects of the invention will appear hereinafter.

The invention consists in the novel parts and combinations of parts to be described herein: after, all'of which contribute to produce an eilicient hydraulic brake apparatus.

A preferred embodiment of the invention is described in the following specification, while the broad scope of the invention in the appended claims.

is pointed out a The drawing is avertical section through a Q master cylinder embodyingmy invention and also showing a reservoir in vertical section indicated as connected to the master cylinder. This view. also illustrates the pipe connection from the cylinder for connecting the same to the brake cylinders at the wheels, the operating pedal being illustrated broken away.

In practicing this invention I provide a master cylinder having two pistons of equal diameter mounted to move in the cylinder, with means connecting the same to enable be advancedinunison. Ialsoprovide-meansmchas lid a foot-operated pedal for advancing the pistons to apply the brakes. These pistons have a position of rest in which the pistons are in their most retracted position and when in this position an inlet port provided in the master cylinder for admitting the operating liquid lies just in advance of the forward piston. This inlet port is also in communication with a by'-pass connection that leads from it back into theinterior of the cylinder back of the forward piston, and in front of the rear piston. With this organization of parts the advance of the rear piston with the forward piston prevents the development of a partial vacuum back of the advancing forward piston, thereby preventing eiliux of the operating liquid from the inlet port into the rear chamber of the cylinder. A suitable pipe connection from thegcylinder is pro vided for connecting the cylinder to the wheel brakes.

, Referring more particularly to the parts, i represents a master cylinder provided with two pistons, namely a forward piston Z and a rear piston 3, said pistons being of equal diameter and connected together by a connecting stem 4 so that they can be advanced in unison. The forward end of the cylinder has a compression chamber 5 which is provided with a suitable connection 6 for connecting it to the pipes that lead the operating liquid to the-hydraulic are indicated in the drawing, the forward piston is located just back of an inlet port 71 that admits the operating liquid into the compression chsmba 5. This inlet port is connected by ivy-pass port 8 to the 9 that n formed in the rear of the cylinder between the pistons. The pistons may be actuated in any suitable manner, preferably by means of. an adjustable connection ii) connecting" to the rear piston and this connection may be actuated by a foot pedal ii oi any suitable constmction.

i prefer to supply the operating liquid to the inlet port by providing a loose it on the upper side of the cylinder at which a threaded pipe connection it may be attached, said ports '1! and d communicating with the chamber Mi formed within this boss.

A sufiicient supply of the operating liquid is insured by providing a reservoir 15 having an outlet connection 96 in its bottom that is connected by a suitable pipe line, indicated by the line ll, to the connection iii. In order to insure that the operating liquid, such as oil, supplied to the master cylinder will be clean, I preler to provide an outlet is in the form of a sleeve that screws down onto a bushing I 8 set in the bottom of the reservoir and this sleeve is provided at an elevated point above the bottom with a plurality of outlet holes 20. The reservoir is constructed so as to enable a pressure to be developed within it slightly above atmospheric pressure. For this purpose the upper end of the is'closerl by a cover 2!] that seats on a 't gusset 22 on the upper edge of the body o the may be forced down onto the gasket by of a stem. is connected at its lower end totheslceve. and has threads 2% at its upper end to receive a nut it that screws onto these threads and seats on the upper face of the cover.

The liouid level in the reservoir is indicated reservoir and this cover at the line 26. In practice, if the liquid level 26 rises by reason of overheating the liquid, then the air chamber 21 will become smaller as the level 26 rises. This air chamber operates as an elastic cushion for the liquid to expand against. If. on cooling, the pressure within the reservoir drops below atmospheric pressure, a small inlet valve 28 will open to admit more air to the reservoir.

This valve 28 comes upon its seat 28 by an upward movement and is normally held closed by a coil spring 30 received in the body of the valve and thrusting against a collar 3| on the upper end of the valve-stem 32. The upper end of the valve body is closed by a screw plug 33 provided with a small air inlet passage 34.

The operating fluid can be supplied to the reservoir l5 through an inlet bushing 35 provided with a removable air-tight screw plug or cap 36.

The connection it from the brake pedal to the pistons preferably includes an adjustable connection 8? of any suitable construction.

The pistons 2 and ii are provided with cup leathers 38 on their forward faces. As these cup leathers are very eflicient in preventing leakage, I provide means for lubricating the rubbing face of the piston 3. removable oiling plug 39 in the cylinder wall that screws into a small oil cup 40 having an oil passage '4! leading down from it to the bore of the cylinder and just over the piston 3.

The lower end of the bushing 35 is below the level of the valve 28. This. it impossible to fill the reservoir completely and insures the vi.

presence or air chamber 2'3.

In the operation or" this apparatus, when the pistons 2 and 3 are moved. in uni right enslof the cylhider. occurs, rear piston 3, ward piston, prevents e her 3 between the piston, s. way vents the development oi a partial vacuum .2 oi the piston 2. In this way it is impossible to develop any suction efiect in the inlet port 1 which would have the, effect of producing an efflux of liquid through this port into the rear chamber of the cylinder. Hence, as the piston 2 advances across the pom l, the pressure in this port and in the compression chamber 6 is maintained. As soon as the port l closes, due to the advance oi the forward piston, the operating pressure inthe compression chamber 5 is developed, and the brakes connected to the pipe connection will be applied. On the return stroke, as the pistons arrive at their position of rest, the piston 2 uncovers the port 7 and reestablishes communication between the compression chamber 6 and the reservoir 65, insuring a plentiful supp y of the operating liquid to the compression chamber.

In apparatus of this kind now used in practice, a relief valve, is sometimes provided on the cover or head 2:] to roaintahi this operating pressure at any point desired.

lit is understood that the embod ment oi the invention described herein is only the many embodiments this invention may i:- re, and I do not wish to be in the proctica of the buvention, nor in the claims, to the particuler embodiment set forth.

I claim is:

i. in hydraulic brake apparatus for automoplies, the combination or a cylinder, two pis- For this purpose I provide a tons of equal diameter mounted to move in the cylinder with means connecting the same for advancement in unison, means connected with the pistons for advancing the same to apply the brakes, said pistons having a position of rest and said cylinder having an inlet port for the operating fluid just in advance of the forward piston when in the said position of rest, and with a passage leading from the inlet port through the cylinder wall into the interior of the cylinder back of the forward piston, whereby the advance of the rear piston with the forward piston maintains a liquid seal back of the advancing forward piston, a pipe connection for connecting the forward end of the cylinder tothe wheel brakes, and a reservoir for theoperating liquid connected with the cylinder and supplying operating liquid to the said inlet port, said reservoir having a closed air chamber above the liquid level-therein.

2. In hydraulic brake apparatus for automohiles, the combination of a cylinder, two pistons of equal diameter mounted to move in the cylinder with means connecting the same for advancement in unison, means connected with the pistons for advancing the same to apply the brakes, said pistons having a position of rest and said cylinder having an inlet port for the operating fluid just in advance of the forward piston when in the said position of rest, and with a passage leading from the inlet port through the cylinder wall into the interior of the cylinder back of the forward piston, whereby the advance of the rear piston with the forward piston maintains a liquid seal back of the advancing forward piston, 'a pipe connection for connecting the forward end of the cylinder to the wheel brakes, and a reservoir for the operating liquid connected with the cylinder and supplying operating liquid to the said inlet port, said reservoir having a closed air chamber above the liquid level therein and having a valve for admitting atmospheric air if the pressure falls below atmospheric pressure.

3. In hydraulic brake apparatus for automobiles, the combination of a cylinder, two pistons of equal diameter mounted to move in the cylinder with means connecting the same for advancement in unison, means connected with the pistons for advancing the same to apply the brakes, said pistons having a position of rest and said cylinder having an inlet port for the operating fluid just in advance of the forward piston when in the said position of rest, and with a passage leading from the inlet port through the wall of the cylinder into the interiorof the cylinder back of the forward piston, whereby the advance] of the rear piston with the forward piston maintains a liquid seal back of the advancing'forward piston, a pipe connection for connecting the forward end of a port, said reservoir having an air chamber with an air check valve opening into the same from the atmosphere, and operating as ,a resilient cushion for the operating liquid.

' EUGENE G. CARROLL. 

